Biology Department, Brookhaven National Laboratory, Upton, New York 11973.
Proc Natl Acad Sci U S A. 1983 Apr;80(7):1933-7. doi: 10.1073/pnas.80.7.1933.
In cultured pea roots there is extrachromosomal DNA associated with cells that differentiate from the G(2) phase of the cell cycle that is absent from those that differentiate from the G(1) phase. We examined this extrachromosomal DNA by electron microscopy and found that it consisted of three types: (i) double-stranded linear molecules with single-stranded branches (74%), (ii) double-stranded molecules without branches (26%), and (iii) free single-stranded molecules. The double-stranded molecules with or without branches were similar in length, having a modal length of 10-15 mum. The free single-stranded molecules were shorter and had a mean length of 3.8 mum. The length of the branches attached to the duplex molecules was only slightly less than that of the free form. The duplex molecules with branches were interpreted as configurations reflecting an ongoing strand-displacement process that results in free single-stranded molecules. Finally, measurements on duplex molecules with multiple branches suggested that the extrachromosomal DNA may exist in the form of tandemly repeated sequences.
在培养的豌豆根中，有与细胞周期 G2 期分化的细胞相关的染色体外 DNA，而与从 G1 期分化的细胞无关。我们通过电子显微镜检查了这种染色体外 DNA，发现它由三种类型组成：（i）带有单链分支的双链线性分子（74%），（ii）没有分支的双链分子（26%）和（iii）游离的单链分子。有或没有分支的双链分子长度相似，模态长度为 10-15 µm。无分支的游离单链分子较短，平均长度为 3.8 µm。连接到双链分子上的分支的长度仅略小于游离形式。带有分支的双链分子被解释为反映正在进行的链置换过程的构型，导致游离的单链分子。最后，对带有多个分支的双链分子的测量表明，染色体外 DNA 可能以串联重复序列的形式存在。
